Explosive fuse-cord

ABSTRACT

An explosive fuse-cord having an inner explosive core and an outer waterproofing sheath of a copolymer of ehtylene and from 7 to 30 percent by weight of the copolymer of vinyl acetate or alkyl acrylate or alkyl methacrylate wherein the alkyl group contains from 1 to 4 carbon atoms.

Langrish-Smith et a1.

[ EXPLOSIVE FUSE-CORD [75] Inventors: Michael Anthony Langrish-Smith,

Barnet, England; Daniel Steele, Stevenston, Scotland [73] Assignee:Imperial Chemical Industries Limited, London, England [22] Filed: Jan.28, 1974 [21] Appl. No.: 437,385

[52] US. Cl 102/27 R [51] Int. Cl. C0bc 5/00 [58] Field of Search 102/27[56] References Cited UNITED STATES PATENTS 3,260,201 7/1966 Kelly et a1102/27 3,382,802 5/1968 Prior et a1 102/27 Feb. 25, 1975 3,407,73110/1968 Evans 102/27 3,712,222 1/1973 Richardson et a] 102/27 3,730,0975/1973 Helfgeni et a1. 102/27 FOREIGN PATENTS OR APPLICATIONS 1,120,2007/1968 Great Britain 102/27 Primary ExaminerVer1in R. PendegrassAttorney, Agent, or FirmCushman, Darby & Cushman [57] ABSTRACT Anexplosive fuse-cord having an inner explosive core and an outerwaterproofing sheath of a copolymer of ehtylene and from 7 to 30 percentby weight of the copolymer of vinyl acetate or aliky] acrylate or alkylmethacrylate wherein the alkyl group contains from 1 to 4 carbon atoms.

10 Claims, N0 Drawings 1 EXPLOSIVE FUSE-CORD This invention relates toan explosive fuse-cord having an improved waterproof thermoplasticssheath.

Explosive-fuse cord normally comprises a core of explosive materialsurrounded by reinforcing wrappings, for example natural or synthetictextile yarns. Thus, detonating cord usually has a core of PETN(pentaerythritol tetranitrate) and safety fuse has a blackpowder core.The core is often encased in a thin envelope of paper or plastics film.Reinforcing yarns are applied around the envelope and a waterproofsheath of thermoplastics is applied over the yarns, usually byextrusion. The waterproof sheath usually consists of plasticisedpolyvinyl chloride (PVC) or polyethylene and the required extrusiontemperature exceeds 160C, which is higher than the melting point of PETN(141C). Thus, there is a substantial risk of excessive heating andignition of PETN during the extrusion process and such incidents havebeen reported. Clearly, it would be advantageous to use sheathingmaterial which can be extruded at a lower temperature.

We have now found that certain copolymers of ethylene and vinyl acetateor alkyl acrylates or alkymethacrylates may be advantageously used forthis purpose. Not only can they be extruded at a lower temperature, butthey give fuse-cords with other deisrable properties.

In accordance with this invention, an explosive fusecord comprises aninner explosive core and an outer water-proofing sheath of a copolymerof ethylene and from 7 to 30 percent by weight of the copolymer of vinylacetate or an alkyl acrylate or an alkyl methacrylate wherein the alkylgroup contains from 1 to 4 surprisingly found that the copolymer used inthis invention enters the interstices in the textile layer during theextrusion and the migration of water through the textile layer islargely prevented. The water resistance of the fuse-cord is therebyimproved. Fuse-cords having especially good water resistance may beprepared when the textile wrappings comprise fibrillated thermoplasticsyarn, for example fibrillated polypropylene. Fibrillated polypropyleneyarn which has been coated with a hot melt adhesive comprising acopolymer of ethylene and vinyl acetate is particularly useful in thisrespect. Examples of such hot melt adhesives are mentioned in WestGerman patent application specification No. 2,203,261.

For certain applications where there is a risk of the fuse-cordacquiring an electrostatic charge, the copolymer sheath may beadvantageously rendered conducting by the incorporation of finelydivided carbon whereby any charge can be readily dissipated to earth.

In addition to the aforementioned advantages, the fuse-cord of theinvention is more flexible at low temperatures and is surprisingly moreabrasion resistant than fuse-cords with sheaths of polyvinyl chloride orpolyethylene. It is therefore more suitable for use in severeconditions, for example in frozen areas and for suspending charges inrough shotholes.

The invention is further illustrated by the following Examples ofdetonating cord, of which Examples 1 and 2 have conventional sheaths ofPVC or polyethylene and are included for comparison, whereas Examples 3to 5 are in accordance with the invention.

The detonating fuse-cords were made by a commonly used fuse-cordmanufacturing method as described, for

carbon atoms. Suitable acrylates and methacrylates in- 5 The preferredcopolymer is a copolymer of ethylene ciystalline PETN loaded at a chargerate of 10 g per and vinyl acetate. The copolymers should preferablymetre Surrounded by a paper tube of 0 18 mm thick have a melt flow indexof from 0.1 to 25 and more pref- The paper tube was Covered with ahelic'auy p i 7 'i p fii s i g g g ggj 40 forcing layer of 10 strands of1,000 denier pin-roll fithe melting point of p y lov'ver than brillatedpolypropylene tape having a width of 2.5 mm that of polyethylene, thecopolymer is conveniently apa thickness 9'8 mm spun at turns inetreplied to the fuse-cord by extrusion, preferably pressure f0 owed y F l fi ayer clonslstmlg of extrusion, high quality extruded sheaths-beingobtained 5 8 Strands O t 8 Same pin-r0 l m med p0 ypropy tape spun at 39turns per metre. A thermoplastlcs at extrusion temperatures much lowerthan those hith- Sheath 0 4 mm thick was extruded around the ol r0 ertonecessary for extruding external sheaths on explolane Us b means of acrosshead g g i sive fuse-cord. Thus, in the manufacture of detonatingg. h f E l 3 t 5 b t d d cord having a core of PETN, the extrusiontemperature c S 5 0 Xamp es 0 emg ex w C can be maintained below themelting point of the er pre su PETN In Example 1 the sheath was PVCplasticised with The fuse-cord advantageously comprises one or more 36parts of di-isooctylphthalate per parts of PVC. reinforcing layers oftextile wrappings wound around In example 2 the sheath was low densitypolyethylene. the explosive core as in the conventional fuse-cords. InExamples 3 to 5 it was a copolymer of ethylene and Textile woundfuse-cords have hitherto had low water 55 vinyl acetate (VA) comprising7 percent, 18 percent resistance largely because of the tendency forwater to and 28 percent respectively by weight of vinyl acetate, migrateby capillary action along the textile layer and the melt flow index ofthe copolymers being 2. The enter the explosive core from the side overlong disproperties of the fuse-cords of Examples are given in tancesfrom a cord end immersed in water. We have the following Table.

TABLE Example l 2 3 4 5 Sheath material llastieised Low DensityEthylene/vinyl Ethylene/vinyl Ethylene/vinyl PVC Polyethylene acetatecopolacetate eopolacetate copo| ymer 28 VA ymer 1892 VA ymer 7ft VAExtrusion head temperature 170C 165C 1 10C C C Abrasion resistance 2.512.8 7.5 16.4

(average No. of passes for puncturing) TABLE- Continued Example 1 2 3 45 Sheath material Plasticised Low Density Ethylene/vinyl Ethylene/vinylEthylene/vinyl PVC Polyethylene acetate copolacetate copolacetatecopolymer 287: VA yrner 18% VA ymer 7% VA Low temperature performanceCold flex temperature 22C 40C 39C 39C Cold bend temperature 45C 70C 70C70C Charpy cmbrittlemcnt tcmpl to 20C 30 to 35C 30 to 35C 30 to -35Ccrature Water resistance 110 cm 110cm 16 cm l7 cm 17 cm (Averagepenetration after 24 hours) Gap propagation 16 mm 16 mm to mm 16 mm 16mm Velocity of detonation 6.8 6.8 6.8 6.8 (1.8 V Tensile strength 100 Kg100 Kg 100 Kg [00 Kg 7 The abrasion resistance was determined bysuspending a length of fuse-cord, with a 3 Kg weight attached to oneend, over the right angled edge of a concrete block whilst the other endwas maintained at an angle of 30 to the horizontal. The cord was passedrepeatedly over the concrete edge until the sheath became punctured. Theaverage number of passes required are given for each sample.

The low temperature performance was measured as the temperature at whichthe sheath became brittle or too stiff to allow lengths of the cord tobe knotted together. The cold flex temperature was determined accordingto British Standard 2782 Part l/l04B/l970, the cold bend temperature wasdetermined according to British Standard 2782 Part l/l04B/l970 and theCharpy embrittlement temperature was determined according to BritishStandard 2782/306E/l970.

The water resistance was determined by vertically suspending lengths offuse-cord with an exposed end immersed under a head of 1.6 metres ofwater for 24 hours and measuring the distances to which water hadpenetrated along the cord.

In the gap propagation test two lengths of fuse-cord were maintaniedparallel and at a measured distance apart with an air gap between them.The maximum distance over which detonation was communicated from onelength to the other was determined.

The test results given in the Table show that the fusecords of Examples3 to were sheathed at a temperature below the melting point of PETN.They were superior in abrasion resistance, water resistance andflexibility to the fuse-cords sheathed with PVC and polyethylene and inexplosive and mechanical properties they were at least equal to thelatter fuse-cords.

What we claim is:

1. An explosive fuse-cord comprising an inner explosive core and anouter waterproofing sheath of a copolymer of ethylene and vinyl acetatecontaining from 7 to 30 percent by weight of the latter.

2. An explosive fuse-cord as claimed in claim 1 wherein the copolymerhas a melt flow index of from 0.1 to 25.

3. An explosive fuse-cord as claimed in claim 1 wherein the copolymer isapplied to the fuse-cord as a pressure extruded sheath.

4. An explosive fuse-cord as claimed in claim 3 wherein the explosivecore is PETN and the sheath is extruded at a temperature below the PETNmelting point.

5. An explosive fuse-cord as claimed in claim 1 comprising reinforcinglayers of textile wrapping wound around the explosive core.

6. An explosive fuse-cord as claimed in claim, 5 wherein the textilewrappings comprise fibrillated thermoplastics yarn.

7. An explosive fuse-cord as claimed in claim 6 wherein the fibrillatedthermoplastics yarn comprises fibrillated polypropylene.

8. An explosive fuse-cord as claimed in claim 7 wherein the fibrillatedpolypropylene yarn is coated with a hot melt adhesive'comprising acopolymer of ethylene and vinyl acetate.

9. An explosive fuse-cord as claimed in claim 1 wherein the copolymersheath contains finely divided carbon.

10. An explosive fuse-cord comprising an inner explosive core ofmeltable material and an outer waterproofing extruded sheath of acopolymer of ethylene and vinyl acetate containing from 7 to 30 percentby weight of the latter, said sheath being extruded around said core ata temperature below the melting point of said core.

Patent No. 3, 7, Dated 5; 975

Michael Anthony LANeRIsH-smm and Daniel STEELE Inventor(s It iscertified that error appears in the above-ideotified patent and thatsaid Letters Patent are hereby corrected as shown below:

. On the front page format after paragraph "[21]", insert:

--[30] Foreign Application Briority Date I February Great ai a o a o a oo a o o o o 0 0 Signed and sealed this 24th day of June 1975.

(SEAL) Att est C. IEARSHALL DANE RUTH C. MASON Commissioner of Patents IAttesting Officer and Trademarks UNITED STATES PATENT OFFICE CERTIFICATEOF CORRECTION Patent No. Dated 5, 975

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

. On the front page format after paragraph [2l]", insert:

-[30] Foreign Application Priority Data I h a o oooooi. on n 000 Signedand sealed this 24th day of June 1975.

SEAL) Attest:

C. MARSHALL DANE-3 Commissioner of Patents and Trademarks I RUTH C.MASON Attesting, Officer

1. AN EXPLOSIVE FUSE-CORD COMPRISING AN INNER EXPLOSIVE CORE AND ANOUTER WATERPROOFING SHEATH OF A COPOLYMER OF ETHYLENE AND VINYL ACETATECONTAINING FROM 7 TO 30 PERCENT BY WEIGHT OF THE LATTER.
 2. An explosivefuse-cord as claimed in claim 1 wherein the copolymer has a melt flowindex of from 0.1 to
 25. 3. An explosive fuse-cord as claimed in claim 1wherein the copolymer is applied to the fuse-cord as a pressure extrudedsheath.
 4. An explosive fuse-cord as claimed in claim 3 wherein theexplosive core is PETN and the sheath is extruded at a temperature belowthe PETN melting point.
 5. An explosive fuse-cord as claimed in claim 1comprising reinforcing layers of textile wrapping wound around theexplosive core.
 6. An explosive fuse-cord as claimed in claim 5 whereinthe textile wrappings comprise fibrillated thermoplastics yarn.
 7. Anexplosive fuse-cord as claimed in claim 6 wherein the fibrillatedthermoplastics yarn comprises fibrillated polypropylene.
 8. An explosivefuse-cord as claimed in claim 7 wherein the fibrillated polypropyleneyarn is coated with a hot melt adhesive comprising a copolymer ofethylene and vinyl acetate.
 9. An explosive fuse-cord as claimed inclaim 1 wherein the copolymer sheath contains finely divided carbon. 10.An explosive fuse-cord comprising an inner explosive core of meltablematerial and an outer waterproofing extruded sheath of a copolymer ofethylene and vinyl acetate containing from 7 to 30 percent by weight ofthe latter, said sheath being extruded around said core at a temperaturebelow the melting point of said core.